Mobile telephone system



Sept. 13, 1949,

Filed March 22, 1946 L. R. JACOBSEN MOBILIE TELEPHONE SYSTEM 2 Shets-Sheet l' SWITGHBOARD 16/ FIG. I.

/' f v lc Id le I;

OSCILLATORS I 2a 2b -2c -24 Ze 2;:

AND MODULATORS suBcARRIER 3A I ss AMPLIFIERS CENTRAL RADIO TRANSMITTER E E L I L L L q FIG. 2.

RECEIVER TRANsMI'ITER I lla I OSCILLATOR FILTER AND [2a MODULATOR l g? LI43 I 3 l I I T- CENT-'RAL REcEIvER -7 FIG. 3.

VIDEO AMPLIFIER VIDEO AMPLIFIER I 9Q\ 9b 9C\ FILTERS Isa 15b L/ISI; I

SWITCHBOARD [6 INVENTOR.

LANCE R. JACOBSEN ATTORNEY P 1949- 1.. R. JACOBSEN 2,481,516

MOBILE TELEPHONE SYSTEM Filed March 22, 1946 2 Sheets-Sheet 2 {3A 35 [3D 3E FIG. 4.

SUBCARRIER I AMPLIFIERS FREQUENCY WA 17B MODULATORS T 1M9 TRANSMITTER TO ANTENNA FROM FREQUENCY MODULATORS FIG. 4A.

SWEEPING RECEIVER I FIG. 5.

- M U r' F2|B l k VIDEO I AMPLIFIERS J INVENTOR.

I LANCE R- JA COE SEN flan/1 )7;

ATTORNEY Patented Sept. 13, 1949 UNITED MOBILE TELEPHONE SYSTEM S PATENT OFFICE The invention described hereinrnaybe ma ufactured and used by or f th'Govimngnffgf governmental purposes, without the payment to me of any royalty thereon.

My invention relates to a multi-channel. radio system forvoice communication, which may per; form the functions of a multi-subscriber telephone system. Because of the radio linksemployed the subscriber ma be mobile within the range of coverage of the radio waves. The channels to the separate subscribers are isolated on a'basis of frequency selection. Provision is made for the connection of my mobile system With the commercial wire line telephone systems. i The same degree of privacy. is preserved as in normal.

telephone subscriber. systems.

It is a purpose of my. invention to providea mobile telephone system having radio links.

It is .anotherfpurpose of my invention .to' provide a mobile telephone system with arrangement for interconnecting it with a wire line telephone system. I

' It is another purpose of m invention to provide a'multi-channel radio transmission and reception system.

It is another purpose of my invention to provide a system. of combined amplitude and frequency modulation by which a multiplicity of voice messages may be impressed and transmitted over a single carrier.

It is another purpose of my invention to provide a system of communication having a multiplicity of channels in a single final amplifier and transmitting antenna and also in a single receiving antenna and receiver. g

The system which is proposed is shown in block diagram in the figures as follows:

{Figure 1 is a block diagram of a central transmitting station.

Figure 2 is a block diagram of a subscriber station.

Figure 3 is a block diagram of a central receiving station.

Figure 4 shows a modification of my invention incorporating a multi-principal carrier system in the central transmitter.

Figure 4A shows one example of a system for sweep tunin the transmitter.

Figure 5 shows a modification of my inventio incorporating a. multi-principal carrier system in the central receiver. I v

-'Ifl 1e feature of; my mobile telephone system which makes possible the multiplicity of channels ..;.the sys emi f modulation which} s a l. new explain.

Considers; principal radio carrier of 300.megacycles frequency: Now frequency modulate .this: principalcarrierby asubcarrier of kilocycles frequency. Let the normal frequency shift of the principal carrier be ijg0; kil0cy1es,-f( r normal mnli de lth s ar ie -v N w le the normal si lbcgarrier be amplitude modulated-by Voice-free. quencies the. -range 250 ;300Q cycles. For per centcmq llllatiqn Pheampl tudeof the .80 ki o: ycl u atr etwil va tom ero. to. twic n r: mal. The eorrespor dingv limiting frequencyshiftsproduced in the principal carrier will. be zero and 20 ki y le c. It i .;a o.-i o. hl t p pose on the .300, megacyo1e principal carrier another subcarrier, of 86 lgilocyeles similarly modulated by voicegfrequeneies; in the range.. 25Q-.3000 cycles. Efiaclisubcarrier and its attendant sidebands of' amplitude modulation will by itselfoc l py aband width .of 600 (i cycles. lt iswell-lgnown 6 art of frequency modue lafioil. that apaifrls i Wi ra I supe o e frequency modulations the band Width whichmust be .passed should be .considerablyin excess of the highestlfrelduenc .of, the .modulation .superposed-Q h s io 'a kilocycle's afband 'wid xinjium, subcarrier .of- :99

i W I, t about theprincip al carrierpjf"200,0(i0t6400fl0 'locycle s would probably beadqqllate, and. in thecase ofth ef360 megafcyole principalicarrie v befyery easilyhan ledintliultrahigh frque cy. radio channels.

Structure to perform .the. above j nctions is show n Fi ure '1, wnicnsfhow ajcentjra traii s mittijng sta: on}. l,A1 idio signals arereceiv the" separate 'audio "lines or channels la, l b, 1c; ta, so inai m. sw t hb ard 6. These "lines a h l ad, "Fatim is 'Tlie s'e oscillators ar each' one;

eta with a r equencysep'aration' of six ilocye esii Each. carrier is V amplitude linodulate'd 'by its own audio signal: j The'jmodulatd carriers fromi'tliej,

number'of channels whichican :b'e aecomm odati'ecl carrieifredueficy and six kilocycle'slbroad rnay. e. pqp q p ql banuin t o iilifir. 3A.lettered-18am transmitter 4 as modulation. In radio transmitl r-and lmqd t r...

I on" subcarrier the signals "are not confused in subcarrier amplifier 3 The ter 4 this modulation frequency modulates the principal carrien The output is radiated from antenna 5. 7

In order to accommodate more audio channels Id, Ie, If, etc., additional oscillators and amplifiers are provided for them, 2d, 26, 2f, etc. These oscillators are respectively on nine additional frequencies in the band 99-153 kilocyclesl Their outputs are combined and amplified in subcarrier amplifier 3B, the pass band of which may be considered as 99-153 kilocycles. The output of amplifier 3B, as well as that of amplifier 3A, is applied as modulation on the carrier in radio transmitter 4. The number of subcarrier amplifiers .which may apply additional subcarriers and the number of voice channels which may be thus .passed through transmitter I and antenna 5 is very large in view of the high frequency of the principal carrier, 300 megacycles.

The signal from antenna 5 isbroadcast and is received on all the receivers at the subscriber stations, one of which is shown in Figure 2. The subscriber receiver IIa is a frequency modulation receiver and is fixed-tuned to the frequency of the principal carrier from the central transmitter. The signal after passing the discriminator of receiver I la will reproduce the modulating frequencies, namely the subcarriers. This signal is passed to a filter I2a which has a band width of six kilocycles and a center frequency equal to that of the subcarrier from oscillator 2a. Accordingly filter I2a selects from .all the subcarriers reproduced by receiver I la just one along with its attendent side bands of modulation,'and that signal only is passed along with the voice modulation which it carries. This signal is amplified and detected in filter I 2a and passed to the telephone receiver I3d, where the voice tones are reproduced. Y e

It is thus seen how a voice communication from a particular channel Ia is transmitted to a particular receiver I 3a of a particular subscriber station by radio. 1 L, V

It is apparent that forjeach'subscriber there must be a separate audio channel Id, Id, etc. Infsofar as calling a subscriber is concerned, channels Ia, Id, etc., may be ordinary lines of a normal subscriber telephone system, with the restriction that ringing should bedone by a lowfrequency alternating current rather than by direct current. Means for such modification are well known in the art.

The apparatus for responding to a call from the central station or initiating a call to the central station from the subscribers station will now be'described.

The subscribers calling signal or voice (as the case may be) is received in oscillator and modulator Ma, Figure 2, which is similar to the oscillators and modulators 2a, 21), etc and the calling signal or voice signal is impressed as amplitude modulation on a subcarrier generated therein. For convenience this subcarriermay be thought of as having the frequency of filter I2a, thougha somewhat different frequency might be preferable. This amplitude-modulated subcarrier! is then impressed-on a principal carrier in 'transmitter IIla and transmitted. The frequency .of the principal carrier of the subscribers trans-- mitters is common to all but issufficiently remote from'the frequency of the'central transmitter so that it does not interfere with reception in the subscribers receivers.

The signal from all the subscribers are then received together on a single'central antenna 6 From each video amplifier the signals are passed to a bank of filters 9a, 9b, 90, etc. These 7 filters are similar to the filter I2a, that is, each filter passes only a single selected subcarrier with its attendant side, bands. 90, etc.. the subcarrier is demodulated and the voice or calling code frequencies are reproduced. These signals are put upon the wire lines I 5a, I5b, I50, etc. These lines may be handled as incoming lines of a normal subscriber telephone system, and pass to switchboard I6.

Thus there has been shown means for transmitting speech and call signals from a central'station to a multiplicity of mobile stations and-for The wire part of the system and the switchboard I6 are normal except that for each radio, subscribers station there is a pair of lines in the switchboard, rather than the single line of all wire systems. One line of a pair carries speech and signal to the subscriberythe other carries speech and signal from the subscriber.

The two lines are switched together. In setting up the connection between two subscribers stations the incoming line from one station is connected to the outgoing line to the other station and vice versa.

The switchboard I6 may be used also to con-" nect Wire telephone subscribers with 'radio subscribers,

In 'order to increase still further the number of subscribers which my. mobile telephone system can accommodate I'have' introduced the modifietc. (amplitude modulated with voice). are im-v pressed as frequency modulationon the 300 megacycle principalcarrier just as before and then further amplified together with similar signals from frequency modulator 1113 and fromother frequency modulators in a sweep-tuned or'sweeping radio transmitter I8 and radiated from sweeping antenna 19.

In exactly similar fashion voice modulated subcarriers from subcarrier amplifiers .3D, 3E,'etc., are impressed as frequency modulation in frequency modulator I IE on a 302 megacycle carrier, and this modulated carrier is passed to sweeping radio transmitter I8 and radiated from sweepingantenna I 9.

It may be seen that the subcarriers in amplifiers 3A, 3B, etc. may duplicate the'frequencies used in subcarrieramplifiers 3D, "3E, since the signalsof one bank are sufficiently isolated from In these filters 9a, 9b,.

assume those of any other bank by being. on different principal carriers. 1.;

. Fora large number of principal carriers sweeping-radio transmitter .I8 and sweeping antenna l9 may be progressively tuned automatically through the band of principal frequencies. This is doneat a rate rapid compared with the-highest voice frequencies to be transmitted. 1

Figure 4A showsthe input'circuit to one stage of radio frequency amplification in sweeping radio transmitterlB, by means of which it may be-progressively tuned automatically through a band of frequencies. This stage receives'thesignal fromthe frequency modulators and its output goes either to the next stage or to the anten- A continuously tuned tank circuit is shown connected to'the grid 3| of radio frequency amplifier tube -32. It consists of condenser 33 in parallel with variable inductor 34. Variable inductor 34 consists of a number of coil sections 35a, 35b, and 350. Each coil section is connected in series with the next coil section and the points of junction are connected to a commutator segment. Thus coil section 35a has one end connecting to the grid 3| and the other end to coil section 351). The junction point connects with the drawing, only coil section 35a isinparallel' with condenser 33; -The inductance of coil sec tion 35a'is chosen to'have a value which will resonate with condenser 33 at one principal carrier frequency and thus the radio frequency amplifier tube 32 is tuned to amplify only that princi pal carrier frequency. As brush 31 is revolved in a clockwise direction, it comes in contact with commutator segment 36b. The inductance in parallel with condenser 33 is then that of coil section 35a and 35b in series. The inductance of coil section 35b is chosen to have a value which when added to that of coil section 35a will cause resonance at the second principal carrier frequency. Thus radio frequency amplifier tube 32 is tuned to amplify a second principal carrier frequency. Continued rotation of brush 3! in a clockwise direction causes it to contact commu tator segment 360 with the consequent tuning of the radio frequency amplifier 32 to a third principal carrier frequency, in "the "same manner "as above stated. As brush 31 continues to be rtated, it will again contact commutator segment 36a and the radio frequency amplifier 32 will be again tuned to selectively amplify the'firs't principal carrier frequency.

It is to be understood that, although only three are shown, as many coil sections and commutator segments may be used as there are principal carrier frequencies. Also, another continuously tuned tank circuit such as shown, may be added to the plate circuit of radio frequency amplifier tube 32, in a manner well known in the art, and may be driven by the same motor 38. This will sharpen the overall tuning of the radio frequency amplifier. Furthermore, as many such radio frequency amplifier stages as are necessary to obtain the desired output power may be used. The frequency of the alternation of the principal carriers depends upon relative brush and commutator segment size and the speed of rotation of motor'- 38.--It is also to be understood that there are other well known ways to alternate-the frequency radiated by a radio frequency transmitter and the embodiment shown in Figure 4A is by way of illustration only andis not to be considered as a limitation upon the invention as recited in the claims. v

For-a small number of principal carriers the transmitter and antennamay-be fixed-tuned with a pass band width broad enough to pass all principal carrierssimultneouslm i In this multi-principal carrier system, the mobile subscriber stations are as before except that the tuning of the'subscriber receivers is distributed-among the principal carrier frequencies fromthe central transmitter 18. Each subscriber receiver lla will-be tuned to the principal carrier of the frequency modulator llA with Which'th'at su'bscribers wire line la is associated in switchboardlfi. Similarly the transmitters of the subscriberstations are now tuned to one'or another of a. set ofprincipal carrier frequencies different from the set used for transmission from the central station.

The modification of the central receiving-station for my multiprincipal carrier" system is shown-in Figure 5.

The signals on the multiplicity of principal car-- riers from the subscriber transmitters Illa, etc.- are all received simultaneously on antenna 5 and sweeping receiver 20 at the centralreceiving station.

receiver 2% may sweep in tuning over the-band at a rate high compared to the highest audio frequency'to be received, but in general it is possible to construct a receiver with a much higher pass band widththan it is to construct a transmitter in the-same range, so that the sweeping feature may not be so necessary.

After conversion to intermediate frequency inreceiver 2e (whether actually sweeping or fixedtuned) the output is fed to a multiplicity of intermediate amplifiers. There will be as many different intermediate frequencies in-sweeping receiver 2!! as there are different principal fre-'- quencies in the subscriber transmitters Ila, etc. Each of the intermediate;amplifiers ZIA; ZlB, etc., is tuned to one of these intermediate frequencies and rejects the others. Thus the prin-' cipal carriers are separated in 'the intermediate stage. The outputs of the intermediate ampli-'-" fiers are fedto limiters and discriminators which produce' the subcarrier groups, these groups are fed to their respective video amplifiers 8A, 8B,

etc., 8D, 8151, etc., just as before.

It is seen that, just as inthe central transmitter each subcarrier frequency may be used once for every principal carrier frequency used,

If necessary to coverthe entire band of- 3 principal carriers from the subscribers, sweeping V 7 -mme ewe dense-tin; r

of my invention. which is the; movies E i L, "In: a radio celephene. system, a radio ":i'IP-Wmifiifl'. section,- a telephone switchboard, a multiplicity *DfflDJ-KJS oi sum scriber radio stations, outgoingiines :LEIQmLMQ switchboard canrymg audio signails 'Isarxespecflve sflbsce'rbers so central transmit er stewed-means for-generdthrg a plurality of tinct subcarrier frequeneiesewh one ofs with one subscriber radio station imeaeh or said groups, mesns-e-t me radio itransmitiierstareien amplitude modulate o audio nequeney sought 110 be transmitted. =re

means at said subscriber radio stations tomeceive said-alternately radiated principal carriersrreencrelrradie receivingstation means,- com-o munication means between said subscriber radio stations and-said central receiv ng radiostation means, lines irom said central receive mg :radio station to :said atelephone switch oard.

2, ln anmuktisuloseriber radio telephone..-slalsizens as .set ,iiorsh in claim wherein said receiving niea'nsat .saiidcsubscriher radio stationscomprises, tuning means \to .select {the principal carrier :35-

ce'iving station means. 1 or v o 4.13 amide r I redid system uses in i. wh remseid redid mm meme b e d hand meeivingi to 'meeime all we iredu my mmie s from the subscriber radio Stations meens m reeenedwnemerec imd radio miue mearrierswim e rleeafllveeneretedzoeeih Y eiieers eschcured-rte. enrimenmedieee-freeueeey p re seen-weer sa dem es e1 aeedies h seeiber do feed the -heie iddmed were re meme; ieiermedieie z reeueuer messes are @demedrdete intermediate frequency amplifier outputs of their nespeedre summer greumi finer means so sep- 7 she ger rw Mae resneewe signed to said group of subserihervradio zfiml'a ql'lfi,

means .120 demodulate the essi gned prineipal goalrier, .means te filter irorn the wave derivedfrom the demodulation -the subearrier jirequeney signed to the subscriber radio station, .unear s 1codemodulate .said .subcarrier ref the :audio signal amplitude modulatedruponrit meens toctransduee said audio signal-into acoustical energy. 3

an a muitisubscriber radio delephoneasystem as *set jorth "inclaim 11; wherein said ncomm n cation means ;between said subscriber mad-i0 {star tions .and -.said (centralreceiving radio r'estation comprises means .to roransduce acoustics energy t raud -.freeuerwe',rmeens r g n rates swear-- rier of ihe ,frequeney assigned to zthesubseniber file fol owing 'xce ereuewe eet record wheradio station; zmeans utozemplitude modmateLsaid subcarrier by the saidaaudioireguencypmeansie generate .a :Dsincipai warrier :difiere'nt drum the principal carrier received, these subscriber radio station generated pri-ncipal- -.carriers zheirx 1& signedvsimilarly oneito eaoh-gmupmf subseriber radiostations {and oi a diffierentrfregueneyiiimn the =nr'in ea1 carrier reeei-xeed by s ide mupi meansito frequency {modulate thec saidzprineiml carrier uby -.-theamplitude .modulated frequency, means tortransmit said zfreqmncy pared with 2.11

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s erd uqrcrrequemres.rnrorile-recommende- '1 w 7 V s @9234? commence-r seei- Freer 

